Ammo to fill a niche
I was thinking of ways to use the Banshee effectively, and noticed a niche that wasn't filled by any of the current ammo types. There are ammo types for close range (greased, incendiary, heatsink), medium range (heavy, burst, charged), and extreme range (lesmok). That's just a generalization, but I'm using it to point out the niche, something between medium and extreme range for most guns. So, here are the stats of the ammo I'm suggesting-
+40% Shell Life, -50% Jitter, -30% Damage, +20% AoE radius [the exact values can be tweaked]
The goal with what I'm calling Galvanized Rounds (since I couldn't think of a better name and the name's less important to me than what it does) is to extend the effective range of certain guns without being the go-to ammo for most of them. If you value precision, you'll still want Heavy Clip. If you value damage or AoE, you'll want Charged or Burst. At close range, you'd be better off using normal ammo. This is just something to give those who value range without being overpowered at the extended range.
It's probably easiest to point out, gun by gun, what benefits from the ammo and which ammo types it competes with.
Guns that benefit
Artemis- One of the guns that benefits most from Galvanized rounds. The Galvanized rounds reduces damage, but increases the chance the AoE will hit stuff, and from farther out. The lack of increased muzzle velocity means that the gunner has to be really skilled to hit at its extended range. You'd still want Burst for anything within normal range, but Galvanized rounds provides a nice alternative.
Gatling- You'd still probably want heavy clip if you can only bring one ammo type, but a gunner could use Galvanized rounds to extend the range and be at least somewhat useful with it prior to the enemy entering heavy clip range.
Light Flak- Sort of competes with heavy clip, but you wouldn't get much use out of the extended range. Probably useless for this gun.
Flamethrower- Galvanized Rounds is pretty much a straight-up buff to the flamer. I think it'll be fine, though.
Carronades- I'm lumping them together because they benefit equally. If you care about precision and maximizing the damage of a carronade, Heavy Clip will likely remain the default ammo, but increasing the effective range at the cost of 30% damage provides an interesting alternative. A gunner who can bring multiple ammo types could bring both! Craziness.
Flare Gun- Including because it technically would benefit from the increased range and precision, but most folks wouldn't load special ammo in it anyway.
Mercury- At the ranges Galvanized rounds allows, you'd probably want lesmok. Probably useless in this gun.
Banshee- Another gun that heavily benefits from Galvanized Rounds. This should be no surprise since this is the gun I was trying to help most with the new ammo. Increased AoE radius, reduced jitter, and increased max range mean it can cause chaos from even farther away. It still requires a good gunner to hit at max extended range, though. It allows you to hit farther out, but other ammo like Burst or Greased would be better at closer ranges. Depends on your strategy.
Hwacha- Potentially interesting alternative to Heavy Clip. You won't hit as often compared to Heavy Clip, but each hit has an increased AoE radius. Not sure the jitter reduction would be enough to hit consistently at max extended range, though. Hard to theorycraft whether it would be worthwhile or not.
Heavy Flak- Needs extra range badly, so a skilled gunner could potentially use this to good effect. Probably not the buff it needs, though.
Mortar, Lumberjack, Harpoon, Mine Launcher- These guns don't really benefit from Galvanized rounds.
Why it isn't OP
At any other range outside its niche, there are superior alternatives, including normal ammo. Within its extended range, things are harder to hit (since it doesn't increase muzzle velocity or dropoff, and jitter is only reduced by 50%) and damage is reduced. It benefits the rocket weapons, flamethrower, and carronades the most, which are some of the least used weapons in the game.
Other suggestions
I'd like to see the banshee given 10-15 more explosive damage in the AoE component of its damage, and a .5 or so reduction to its jitter. It's a fairly underutilized weapon, and increased damage and accuracy would probably help it see wider adoption.
The Artemis could use a little more zoom to make it a bit easier to use (maybe increase to 2.5x zoom?). It's pretty difficult to use effectively with its current zoom levels.